Ruling on Depending on Mobile Applications to Determine Prayer Times

Many Muslims throughout the world utilize mobile apps to determine prayer times. However, I found that there is difference between the times of prayer offered by these apps and those applied in the Islamic countries. What is the ruling of Sharia on utilizing these apps to determine the times of prayer? 

A Person is Recommended to Answer the Call of (Athan and Iqamaa) as soon as any is Heard

Are the supplications of Athan pronounced after Iqamaa as well?

Stretching Adhan is Disliked

What is the ruling on stretching the words of Adhan (call to prayer) and prolonging it? Is the form in which Adhan is called in mosques disliked to the extent that Muezzins are advised to leave it?

What is the ruling on loudly sending prayers on the Prophet (PBUH ) after Athaan?

Is it permissible for a person who hasn`t made ablution to call for prayer (Adhan)?

Ruling on Unifying the Adhan

What is the ruling on the unification of Adhan?